Ultrasonic transducer

ABSTRACT

Ultrasonic transducers that are capable of generating increased levels of ultrasound, as well as receiving ultrasonic waves with increased sensitivity. The ultrasonic transducers include a back cover, a protective front cover, a backplate, and a vibrator film layer disposed between the backplate and the protective front cover. The backplate includes a plurality of grooves formed on a surface thereof facing the vibrator film layer. Each groove includes upper edges having cross-sectional contours that gradually tend toward the deepest part of the groove to allow a larger area of the backplate to be closer to the vibrator film layer, thereby increasing the resulting electric field, and, consequently, increasing the output power and sensitivity of the ultrasonic transducer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.16/214,889 filed Dec. 10, 2018 entitled ULTRASONIC TRANSDUCER, which isa divisional of U.S. patent application Ser. No. 15/623,780 filed Jun.15, 2017 entitled ULTRASONIC TRANSDUCER, which is a divisional of U.S.patent application Ser. No. 14/442,078 filed May 11, 2015 entitledULTRASONIC TRANSDUCER, which claims benefit of the priority ofInternational Patent Application No. PCT/US2013/045365 filed Jun. 12,2013 entitled ULTRASONIC TRANSDUCER, which claims benefit of thepriority of U.S. Provisional Patent Application No. 61/658,452 filedJun. 12, 2012 entitled ULTRASONIC TRANSDUCER.

TECHNICAL FIELD

The present application relates generally to acoustic transducers, andmore specifically to high performance ultrasonic transducers capable ofgenerating increased levels of ultrasound, as well as receivingultrasonic waves with increased sensitivity.

BACKGROUND

Ultrasonic transducers are known that have a laminated construction,enabling the formation of multiple, generally circular ultrasonictransducers (e.g., up to about 80 or more) in an ultrasonic transducerarray. Such ultrasonic transducers can include first and secondinsulative retaining layers, and a vibrator film layer sandwichedbetween the respective first and second retaining layers. The firstretaining layer can include a first plurality of circular aperturesformed therethrough and the second retaining layer can include a secondplurality of circular apertures formed therethrough, in which the secondplurality of apertures is substantially in registration with the firstplurality of apertures. Such ultrasonic transducers can further includefirst and second cover portions, and the combination of the firstretaining layer, the vibrator film layer, and the second retaining layercan be sandwiched between the first and second cover portions.

In the ultrasonic transducers described above, the side of the vibratorfilm layer facing the first retaining layer is typically unmetallized,and the opposite side of the vibrator film layer facing the secondretaining layer is typically metallized. The ultrasonic transducer canfurther include a plurality of circular, electrically conductivebackplates and a plurality of electrically conductive coil springs,which can be disposed between the first cover and the vibrator filmlayer in substantially the same plane as the first retaining layer. Eachcircular backplate is substantially in registration with respectivecircular apertures formed through the first and second retaining layers.Further, each circular backplate typically includes a plurality ofgrooves, such as V-shaped grooves or trapezoid-shaped grooves, formed onsurface thereof. The plurality of grooves are typically machined,etched, or stamped on the backplate surface, and are typicallyfabricated to have sharp corners and/or edges and straight sides. Eachcoil spring is disposed between a respective backplate and the firstcover. The coil springs are both mechanically and electrically connectedto respective backplates and the first cover, which has an electricallyconductive surface. The first cover portion, the coil springs, therespective circular backplates, and the combination of the firstretaining layer, the vibrator film layer, and the second retaininglayer, are configured to cause the coil springs to urge the circularbackplates against the unmetallized side of the vibrator film layerthrough the respective circular apertures.

With further regard to the ultrasonic transducers described above, thecombination of the electrically conductive first cover, the coilsprings, and the circular backplates forms a first electrode, and themetallized side of the vibrator film layer forms a second electrode. Theultrasonic transducers are configured to allow a voltage to be appliedbetween the first and second electrodes, thereby generating an electricfield between the vibrator film layer and the backplates that causes thefilm to be attracted to the respective backplates. In the event thevoltage applied between the first and second electrodes is AC, the filmcan vibrate, in a transmitting mode, to generate compression waves atsonic or ultrasonic frequencies. In a receiving mode, incoming acousticwaves impacting the ultrasonic transducer are converted to a voltagewaveform.

SUMMARY

In accordance with the present application, ultrasonic transducers aredisclosed that are capable of generating increased levels of ultrasound,as well as receiving ultrasonic waves with increased sensitivity.

In one aspect, the disclosed ultrasonic transducers each include a backcover, a protective front cover, a backplate, one or more springs (e.g.,leaf springs), and a vibrator film layer disposed between the backplateand the protective front cover. For example, a plurality of suchultrasonic transducers (e.g., up to about 8 or more) can be implementedin an ultrasonic transducer array. The backplate can be rectangular,square, hexagonal, or any other suitable geometric shape, and can bemade of metal, an insulative material coated with metal, or any othersuitable material. The side of the vibrator film layer facing theprotective front cover is metallized, and the opposite side of thevibrator film layer facing the backplate is unmetallized. The springsare configured to urge the backplate against the unmetallized side ofthe vibrator film layer. The backplate forms, at least in part, a firstelectrode, and the metallized side of the vibrator film layer forms asecond electrode. The ultrasonic transducer is configured to allow avoltage to be applied between the first and second electrodes, therebygenerating an electric field between the vibrator film layer and thebackplate that causes the film to be attracted to the backplate. In theevent the voltage applied between the first and second electrodes is AC,the film can vibrate, in a transmitting mode, to generate compressionwaves at sonic or ultrasonic frequencies corresponding to a specificsignal waveform. In a receiving mode, incoming acoustic waves impactingthe ultrasonic transducer are converted to a voltage waveform.

In an exemplary aspect, the backplate includes a plurality of groovesformed on a surface thereof facing the vibrator film layer. For example,the plurality of grooves can be elongated linear grooves, circulargrooves, dimple-shaped grooves, or any other suitably shaped grooves.Each groove includes upper edges having cross-sectional contours thatgradually slope, incline, angle, or tend toward the deepest part of thegroove to allow a larger area of the backplate surface, and thus thefirst electrode formed, at least in part, by the backplate, to be nearthe vibrator film layer, thereby increasing the resulting electricfield, and, consequently, increasing the output power and sensitivity ofthe ultrasonic transducer. Because air can become trapped between thegrooves of the backplate and the vibrator film layer, potentiallycausing a reduction in the output power, the backplate can include anair bleed channel configured to allow such air to be released. The airbleed channel can be implemented across the backplate surface,intersecting the plurality of grooves, to release any air trapped in thegrooves at one or more edges of the backplate or through one or bothsides of the backplate.

In a further exemplary aspect, the plurality of grooves on the backplatesurface can each include at least one electrically conductive pillarstructure (e.g., a T-shaped pillar structure) extending from the deepestpart of the groove up toward the vibrator film layer to allow an evenlarger area of the first electrode formed, at least in part, by thebackplate to be closer to the vibrator film layer, thereby furtherincreasing the output power and sensitivity of the ultrasonictransducer.

Other features, functions, and aspects of the invention will be evidentfrom the Detailed Description that follows.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate one or more embodiments describedherein and, together with the Detailed Description, explain theseembodiments. In the drawings:

FIG. 1 is a diagram of a conventional ultrasonic transducer;

FIG. 2 is a diagram of an exemplary ultrasonic transducer, in accordancewith the present application;

FIGS. 3a-3d are depictions of exemplary implementations of theultrasonic transducer of FIG. 2;

FIGS. 4a-4d are cross-sectional views of exemplary grooves that can beformed on a surface of a backplate in the ultrasonic transducer of FIG.2;

FIG. 5 is a diagram of an exemplary pillar structure that can beimplemented in the grooves of FIGS. 4a-4d ; and

FIG. 6 is a block diagram of an exemplary parametric audio systemincluding the ultrasonic transducer of FIG. 2.

DETAILED DESCRIPTION

The disclosures of U.S. patent application Ser. No. 16/214,889 filedDec. 10, 2018 entitled ULTRASONIC TRANSDUCER, U.S. patent applicationSer. No. 15/623,780 filed Jun. 15, 2017 entitled ULTRASONIC TRANSDUCER,U.S. patent application Ser. No. 14/442,078 filed May 11, 2015 entitledULTRASONIC TRANSDUCER, International Patent Application No.PCT/US2013/045365 filed Jun. 12, 2013 entitled ULTRASONIC TRANSDUCER,and U.S. Provisional Patent Application No. 61/658,452 filed Jun. 12,2012 entitled ULTRASONIC TRANSDUCER, are hereby incorporated herein byreference in their entirety.

Ultrasonic transducers are disclosed that are capable of generatingincreased levels of ultrasound, as well as receiving ultrasonic waveswith increased sensitivity. The disclosed ultrasonic transducers includea back cover, a protective front cover, a backplate, one or moresprings, and a vibrator film layer disposed between the backplate andthe protective front cover. The backplate includes a plurality ofgrooves formed on a surface thereof facing the vibrator film layer. Eachgroove includes upper edges having cross-sectional contours thatgradually slope, incline, angle, or tend toward the deepest part of thegroove to allow a larger area of the backplate to be closer to thevibrator film layer, thereby increasing a resulting electric field, and,consequently, increasing the output power and sensitivity of theultrasonic transducer.

FIG. 1 depicts a conventional ultrasonic transducer 100 having alaminated construction, enabling the formation of multiple, generallycircular ultrasonic transducers (e.g., up to about 80 or more) in anultrasonic transducer array. The ultrasonic transducer 100 includesfirst and second insulative retaining layers 104, 108, and a vibratorfilm layer 106 sandwiched between the respective retaining layers 104,108. The first retaining layer 104 can include a first plurality ofcircular apertures 135 formed therethrough and the second retaininglayer 108 can include a second plurality of circular apertures 139formed therethrough, in which the second plurality of apertures 139 issubstantially in registration with the first plurality of apertures 135.The ultrasonic transducer 100 further includes first and second coverportions 102, 110, and the combination of the first retaining layer 104,the vibrator film layer 106, and the second retaining layer 108 issandwiched between the first and second cover portions 102, 110.

In the conventional ultrasonic transducer 100, the side 106.1 of thevibrator film layer 106 facing the first retaining layer 104 isunmetallized, and the opposite side 106.2 of the vibrator film layer 106facing the second retaining layer 108 is metallized. The ultrasonictransducer 100 further includes a plurality of circular, electricallyconductive backplates 116 and a plurality of electrically conductivecoil springs 114, which are disposed between the first cover 102 and thevibrator film layer 106 in substantially the same plane as the firstretaining layer 104. Each circular backplate 117 is substantially inregistration with circular apertures 105, 109 formed through the firstand second retaining layers 104, 108, respectively. Further, eachcircular backplate 117 typically includes a plurality of grooves, suchas V-shaped grooves or trapezoid-shaped grooves, formed on surfacethereof. The plurality of grooves are typically machined, etched, orstamped on the backplate surface, and are typically fabricated to havesharp corners and/or edges and straight sides. Each coil spring 115 isdisposed between a respective backplate 117 and the first cover 102. Thecoil spring 115 is both mechanically and electrically connected to therespective backplate 117 and the first cover 102, which has anelectrically conductive surface. The first cover 102, the coil spring115, the respective circular backplate 117, and the combination of thefirst retaining layer 104, the vibrator film layer 106, and the secondretaining layer 108, are configured to cause the coil spring 115 to urgethe circular backplate 117 against the unmetallized side 106.1 of thevibrator film layer 106 through the respective circular aperture 105.

With further regard to the conventional ultrasonic transducer 100, thecombination of the electrically conductive first cover 102, theplurality of coil springs 114, and the plurality of circular backplates116 forms a first electrode, and the metallized side 106.2 of thevibrator film layer 106 forms a second electrode. The ultrasonictransducer 100 is configured to allow a voltage to be applied betweenthe first and second electrodes, thereby generating an electric fieldbetween the vibrator film layer 106 and the backplates 116 that causesthe film 106 to be attracted to the backplates 116. In the event thevoltage applied between the first and second electrodes is AC, the film106 can vibrate, in a transmitting mode, to generate compression wavesat sonic or ultrasonic frequencies. In a receiving mode, incomingacoustic waves impacting the ultrasonic transducer 100 are converted toa voltage waveform. It is noted that a transducer drive signal can beapplied to the ultrasonic transducer 100 via a connection cable 118.

FIG. 2 depicts an illustrative embodiment of an exemplary ultrasonictransducer 200, having a laminated construction, which is capable ofgenerating increased levels of ultrasound, as well as receivingultrasonic waves with increased sensitivity, in accordance with thepresent application. As shown in FIG. 2, the ultrasonic transducer 200includes a back cover 202, a protective front cover 208, a backplate204, one or more springs 203 (e.g., leaf springs), and a vibrator filmlayer 206 disposed between the backplate 204 and the protective frontcover 208. For example, the backplate 204 may be rectangular, square,hexagonal, or any other suitable geometric shape, may be made of metal,an insulative material coated with metal, or any other suitablematerial, and may be between about 1.2 in.sup.2 to 25 in.sup.2, or anyother suitable size. Further, a plurality of such ultrasonic transducers(e.g., up to about 8 or more) can be implemented in an ultrasonictransducer array. The side 206.1 of the vibrator film layer 206 facingthe protective front cover 208 is metallized, and the opposite side206.2 of the vibrator film layer 206 facing the backplate 204 isunmetallized. The springs 203 are configured to urge the backplate 204against the unmetallized side 206.2 of the vibrator film layer 206. Thebackplate 204 forms, at least in part, a first electrode, and themetallized side 206.1 of the vibrator film layer 206 forms a secondelectrode. The ultrasonic transducer 200 is configured to allow avoltage to be applied between the first and second electrodes, therebygenerating an electric field between the vibrator film layer 206 and thebackplate 204 that causes the film 206 to be attracted to the backplate204. In one embodiment, the vibrator film layer 206 can be grounded forincreased safety and electromagnetic shielding. In the event the voltageapplied between the first and second electrodes is AC, the film 206 canvibrate, in a transmitting mode, to generate compression waves at sonicor ultrasonic frequencies corresponding to a specific signal waveform.In a receiving mode, incoming acoustic waves impacting the ultrasonictransducer 200 are converted to a voltage waveform.

As further shown in FIG. 2, the backplate 204 includes a plurality ofgrooves 205 formed on a surface thereof facing the vibrator film layer206. For example, the plurality of grooves 205 can be elongated lineargrooves formed in substantially parallel rows on the backplate surface(as shown in FIG. 2), circular grooves, dimple-shaped grooves, or anyother suitably shaped grooves. Each linear groove 205 includes opposingupper edges having cross-sectional contours that gradually slope,incline, angle, or tend toward the deepest part of the groove 205 toallow a larger area of the first electrode formed, at least in part, bythe backplate 204 to be closer to the vibrator film layer 206, therebyincreasing the resulting electric field, and, consequently, increasingthe output power and sensitivity of the ultrasonic transducer 200. Inone embodiment, the groove 205 can have one or more walls with one ormore radiused, sloped, inclined, or angled portions. For example, one ormore walls of the groove 205 may be configured to have varying slopes,e.g., a shallower slope, incline, or angle at, near, or toward the upperedges of the groove 205, and to have a steeper slope, incline, or angleat, near, or toward the deepest part of the groove 205. Further, theshallower sloped, inclined, or angled portion of at least one of thegroove walls may be close to parallel to the vibrator film layer 206 at,near, or toward the upper edges of the respective groove(s).

Because air can become trapped between the linear grooves 205 of thebackplate 204 and the vibrator film layer 206, potentially causing areduction in the output power, the backplate 204 includes an air bleedchannel 310 (see FIGS. 3b and 3c ) configured to allow such air to bereleased. The air bleed channel 310 can be implemented across thesurface of the backplate 204, substantially perpendicular to andintersecting the rows of elongated linear grooves 205, to release anyair trapped in the grooves 205 at opposing edges 312.1, 312.2 (see FIGS.3b and 3c ) of the backplate 204, or through one or both sides 204.1,204.2 of the backplate 204. In one embodiment, at least some of thelinear grooves 205 can be open-ended at one or more edges of thebackplate 204 to release such trapped air.

FIGS. 3a-3d depict exemplary implementations of the ultrasonictransducer 200 of FIG. 2. Such exemplary implementations can include anultrasonic transducer array 300 shown in partial construction in FIG. 3a. The ultrasonic transducer array 300 can include two ultrasonictransducers having rectangular backplates 304 a, 304 b, respectively,disposed in a frame 320. FIG. 3a depicts the sides 204.2 (see FIG. 2) ofthe respective backplates 304 a, 304 b that would normally face the backcover 202 (see FIG. 2). FIG. 3a further depicts a spring 303 (e.g., aleaf spring) that can be disposed in any suitable configuration betweenthe respective backplates 304 a, 304 b and the back cover 202. In oneembodiment, two such springs 303 are coupled to the frame 320 anddisposed between the backplate 304 a and the back cover 202, and,likewise, two such springs 303 are coupled to the frame 320 and disposedbetween the backplate 304 b and the back cover 202. In anotherembodiment, a generally flat Z-shaped spring can be configured to engageeach backplate 304 a, 304 b against the vibrator film layer 206 (seeFIG. 2) gently, but evenly, across the vibrator film layer surface.

In one embodiment, the respective backplates 304 a, 304 b, including thelinear grooves 305, can be fabricated using low cost techniques such asextrusion, roll forming, stamping, or machining. In a furtherembodiment, the backplates 304 a, 304 b may be made of plastic (or anyother suitable material) and coated with aluminum (or any other suitablemetallization), thereby lending itself to low cost injection moldingfabrication techniques.

FIG. 3b depicts the side 204.1 (see FIG. 2) of one of the rectangularbackplates 304 a, 304 b that would normally face the vibrator film layer206 (see FIG. 2). As shown in FIG. 3b , the rectangular backplate 304includes a plurality of elongated linear grooves 305 formed in rows on asurface thereof. In one embodiment, the rows of linear grooves 305 onthe backplate surface run along the longer area dimension of therectangular backplate 304, as shown in FIG. 3b . In another embodiment,the rows of linear grooves 305 on the backplate surface run along theshorter area dimension of the rectangular backplate 304. In a furtherembodiment, the rows of linear grooves 305 on the backplate surface runalong the longer or shorter area dimension of the rectangular backplate304, extending substantially to the edges of the backplate 304.

As further shown in FIG. 3b , the backplate 304 includes the air bleedchannel 310 configured to allow any air trapped in the linear grooves305 to be released. In one embodiment, the air bleed channel 310 isimplemented across the surface of the backplate 304, substantiallyperpendicular to and intersecting the rows of elongated linear grooves305, to release any air trapped in the grooves 305 at the opposing edges312.1, 312.2 of the backplate 304, or through one or both sides 204.1,204.2 (see FIG. 2) of the backplate 304. In one embodiment, all fouredges of the rectangular backplate 304 are radiused to keep any sharpcorners and/or edges from inadvertently abrading the vibrator film layer206 (see FIG. 2). FIG. 3c depicts a detailed view of one corner of therectangular backplate 304, showing a portion of the plurality of lineargrooves 305, and the air bleed channel 310 substantially perpendicularto and intersecting the rows of linear grooves 305, and extendingsubstantially to the edge 312.1 of the backplate 304.

FIG. 3d depicts another view of the ultrasonic transducer array 300shown in partial construction. Specifically, FIG. 3d depicts the frame320, the general locations of the rectangular backplates 304 a, 304 b, aprotective front cover 308, and a vibrator film layer 306 sandwichedbetween the rectangular backplates 304 a, 304 b and the protective frontcover 308. In one embodiment, the protective front cover 308 can beimplemented in the form of a protective mesh. To avoid having theprotective mesh 308 inadvertently come in contact with the vibrator filmlayer 306, the ultrasonic transducer array 300 can include at least onesupport bar 309 disposed across at least one area dimension of theultrasonic transducer array 300 and between the protective mesh 308 andthe vibrator film layer 306. In the event an object (e.g., a person'sfinger) comes in contact with the protective mesh 308, the protectivemesh 308 may impinge upon the support bar 309 without contacting thevibrator film layer 306. In one embodiment, a suitable amount ofadhesive-backed felt may be attached to the vibrator film layer 306 toprevent the protective mesh 308 from directly contacting the vibratorfilm layer 306.

FIGS. 4a-4d are cross-sectional views of exemplary grooves 405 a, 405 b,405 c, 405 d, respectively, which can be formed on a surface of abackplate in the ultrasonic transducer 200 of FIG. 2. As shown in FIGS.4a-4d , the cross-sectional geometry of the respective grooves 405 a,405 b, 405 c, 405 d can be made to alternate or vary with respect toeach groove or specified sets of grooves to optimize bandwidth andfrequency response.

In general, the highest forces from the backplate 206 of the ultrasonictransducer 200 are generated near the upper edges of each groove 205,where the first electrode, formed, at least in part, by the backplate204, is nearest the vibrator film layer 206. This is the region thatgives rise to the most displacement. To increase sensitivity, themaximal amount of force as possible should be applied to the vibratorfilm layer 206. It is noted, however, that a typical ultrasonictransducer may saturate due to the vibrator film layer 206 reaching itselastic limit, or due to the dielectric strength of the air. The case ofthe vibrator film layer 206 reaching its elastic limit can be observedfrom the differences in maximum amplitude for varying thicknesses of thevibrator film layer 206. For any output voltage, it is possible toobtain a higher output (in saturation) for a thinner vibrator film layer206 as opposed to a thicker vibrator film layer 206. Once the vibratorfilm layer 206 reaches its elastic limit, there can be a significantchange in modulus, preventing any higher output.

In order to maximize displacement while minimizing the modulus, thegrooves 405 a, 405 b, 405 c, 405 d (see FIGS. 4a-4d ) are made as wideas possible (while considering the total force applied), while avoidinghigher resonance modes in the vibrator film layer. Further, the wallangles of the grooves 405 a, 405 b, 405 c, 405 d are gradually sloped orinclined to keep the first electrode as close to the vibrator film layeras possible over the maximum area. In one embodiment, each groove 405 a,405 b, 405 c, 405 d can include opposing upper edges havingcross-sectional contours that gradually tend toward the deepest parts422 a, 422 b, 422 c, 422 d of the respective grooves, allowing a largerarea of the first electrode to be closer to the vibrator film layer.This maximizes the force on the vibrator film layer (approximatelyinversely proportional to distance), leading to maximal displacement andsensitivity. In another embodiment, each groove 405 a, 405 b, 405 c, 405d can have one or more walls with one or more radiused, sloped,inclined, or angled portions. For example, one or more walls of thegroove 405 a, 405 b, 405 c, 405 d may be configured to have varyingslopes, e.g., a shallower slope, incline, or angle at, near, or towardthe upper edges of the groove, and to have a steeper slope, incline, orangle at, near, or toward the deepest part of the groove.

FIG. 4a depicts a cross-sectional view of the groove 405 a, which has acatenary shape to better conform to the average displacement of avibrator film layer 406 a under biasing, thereby assuring that thevibrator film layer 406 a is as close as possible to the backplate 404 aover its entire surface.

It is noted that a lack of depth in a groove may significantly raise theresonance frequency, which may need to be compensated. With reference toFIG. 4b , instead of using a thicker vibrator film layer 406 b (whichwould increase bending stiffness and likely reduce maximum output), alarger volume of air may be allowed into the groove 405 b forcompliance, thereby reducing resonance frequency. Depending onmanufacturing constraints, such a larger volume of air in the groove 405b can be provided by forming a deeper depression in the center 422 b ofthe groove 405 b with a sloped contour to ensure even air pressuredistribution. As shown in FIG. 4b , the vibrator film layer 406 b isvery close to the backplate 404 b at most points, while providing alarger volume of air in the groove 405 b to reduce the resonancefrequency.

Such a larger volume of air can also be provided using a segmentedgroove 405 c with at least two distinct gradually sloping areas 424 c,426 c, as depicted in FIG. 4c . Because electric field strength isinversely proportional to the distance between the two electrodes (e.g.,the metallized surface of the vibrator film layer 406 c, and the surfaceof the backplate 404 c), the electric field, and therefore the force onthe film 406 c, is highest near the gradual slopes 424 c. The steeperslopes 426 c provide a cavity for acoustic compliance, and contributeless to the overall output.

Another approach is to use a trapezoidal-shaped groove 405 d withradiused, sloped, angled, or inclined opposing upper edges 428 c. Thepresence of the additional electrode area near the vibrator film layer406 d provides more force when the ultrasonic transducer istransmitting, and more sensitivity when the ultrasonic transducer isreceiving. For example, the opposing upper edges 428 c may be radiusedto be greater than 1 mil, greater than 2 mil, about +/−3 mil, or anyother suitable value. In one embodiment, the opposing upper edges 428 cmay have substantially equal varying slopes to allow an increased areaof the surface of the backplate 404 d to be near the vibrator film layer406 d.

FIG. 5 depicts an exemplary electrically conductive pillar structure 530that can be implemented in a groove 505, as well as any of the grooves405 a, 405 b, 405 c, 405 d of FIGS. 4a-4d . Such use of the pillarstructure 530 allows an increased area of the electrode formed, at leastin part, by the backplate 504, to be nearer to the vibrator film layer506, thereby generating more force.

FIG. 6 depicts an exemplary parametric audio system 600, in which anultrasonic transducer 618 conforming to the ultrasonic transducer 200 ofFIG. 2 may be employed. As shown in FIG. 6, the ultrasonic transducer618 is driven by a signal generator 602, which includes an ultrasoniccarrier signal generator 612 and one or more audio signal sources604.1-604.n. Optional signal conditioning circuits 606.1-606.n receiverespective audio signals generated by the audio signal sources604.1-604.n, and provide conditioned audio signals to a summer 608. Itis noted that such conditioning of the audio signals may alternativelybe performed after the audio signals are summed by the summer 608. Ineither case, the conditioning typically comprises a nonlinear inversionnecessary to reduce or effectively eliminate distortion in thereproduced audio. The conditioning may additionally comprise standardaudio production routines such as equalization (of audio) andcompression.

A modulator 610 receives a composite audio signal from the summer 608and an ultrasonic carrier signal from the carrier generator 612, andmodulates the ultrasonic carrier signal with the composite audio signal.The modulator 610 is preferably adjustable in order to vary themodulation index. Amplitude modulation by multiplication with a carrieris preferred, but because the ultimate goal of such modulation is toconvert audio-band signals into ultrasound, any form of modulation thatachieves that result may be employed.

The modulator 610 provides the modulated carrier signal to a matchingfilter 614, which is configured to compensate for the generally non-flatfrequency response of a driver amplifier 616. The matching filter 614provides the modulated carrier signal to the driver amplifier 616,which, in turn, provides an amplified version of the modulated carriersignal to the ultrasonic transducer 618. The ultrasonic beam output,which comprises the high intensity ultrasonic carrier signalamplitude-modulated with the composite audio signal, is demodulated onpassage through the air due to the nonlinear propagation characteristicsof the propagation medium to generate audible sound.

Having described the above exemplary embodiments of the disclosedsystems and methods, other alternative embodiments or variations may bemade. For example, with reference to the linear grooves 405 a, 405 b,405 c, 405 d illustrated in FIGS. 4a-4d , the air gap can be replacedwith a tube of air, a passive radiator, or any other suitable masselement to lower the resonant frequency. The electrode formed, at leastin part, by the backplate can also be made to extend from the deepestpart of the groove, and can be at least partially configured as apillar, a ring, a tube, a T-shape, or any other suitable shape, to bringthe electrode closer to the film. In addition, to assist in filmengagement, the backplate can be configured to be curved (bowed) suchthat it is convex relative to the linear grooves, e.g., ranging fromabout 0.002 inches to 0.100 inches over about a 6-inch span.

It will be appreciated by those of ordinary skill in the art thatfurther modifications to and variations of the above-describedultrasonic transducers may be made without departing from the inventiveconcepts disclosed herein. Accordingly, the invention should not beviewed as limited except as by the scope and spirit of the appendedclaims.

What is claimed is:
 1. A parametric audio system for generating at leastone airborne audio beam, comprising: at least one audio signal sourceconfigured to provide at least one audio signal; at least one signalconditioner configured for receiving the at least one audio signal andfor nonlinearly processing the audio signal to provide at least onepre-distorted signal; a modulator configured to receive thepre-distorted signal and to convert the pre-distorted signal intoultrasonic frequencies; and at least one ultrasonic transducerconfigured to receive the converted signal and to project the convertedsignal through the air along a selected path, thereby invertingdistortion in the projected signal and regenerating the audio signalalong at least a portion of the selected path with reduced netdistortion, wherein the at least one ultrasonic transducer includes: avibrator film layer; and a backplate disposed against the vibrator filmlayer, wherein the backplate includes a plurality of depressions formedon a surface thereof facing the vibrator film layer, and wherein atleast some of the plurality of depressions include opposing sides withupper surfaces having cross-sectional contours with substantially equalvarying slopes to allow an increased area of the surface of thebackplate to be near the vibrator film layer.
 2. The parametric audiosystem of claim 1 wherein the at least one ultrasonic transducer furtherincludes a channel implemented across the surface of the backplate,intersecting at least some of the plurality of depressions, therebyallowing any air trapped in the respective depressions to be released.3. The parametric audio system of claim 1 wherein at least some of theplurality of depressions have at least one open end to allow any airtrapped in the respective depressions to be released.
 4. The parametricaudio system of claim 1 wherein at least some of the plurality ofdepressions include an electrically conductive pillar structureextending from the deepest part of the respective depressions toward thevibrator film layer.
 5. The parametric audio system of claim 1 whereinthe backplate has one of a rectangular, hexagonal, and square geometricshape.
 6. The parametric audio system of claim 1 wherein at least someof the plurality of depressions include the upper surfaces havingcross-sectional contours with varying slopes that gradually tend towardthe deepest part of the respective depressions.